feat: impl diff function for fvm_ipld_amt (#1788)

Add a method for diffing two AMTs. This method only works with AMTs with equal bitwidths.

Author: hanabi1224

Cargo.lock

@@ -22,6 +22,8 @@ go-interop = []
 
 [dev-dependencies]
 criterion = "0.5.1"
+quickcheck = "1"
+quickcheck_macros = "1"
 
 [[bench]]
 name = "amt_benchmark"

ipld/amt/Cargo.toml

@@ -23,8 +23,8 @@ use crate::{
 #[derive(Debug)]
 #[doc(hidden)]
 pub struct AmtImpl<V, BS, Ver> {
-    root: RootImpl<V, Ver>,
-    block_store: BS,
+    pub(super) root: RootImpl<V, Ver>,
+    pub(super) block_store: BS,
     /// Remember the last flushed CID until it changes.
     flushed_cid: Option<Cid>,
 }
@@ -78,7 +78,7 @@ where
         }
     }
 
-    fn bit_width(&self) -> u32 {
+    pub(super) fn bit_width(&self) -> u32 {
         self.root.bit_width
     }